Electron tube apparatus having grid consisting of vanes, projecting into electron beam, tapered to reduce beam interception



March 29, 1966 A. J. FIEDOR ETAL v ELECTRON TUBE APPARATUS HAVING GRID CONSISTING OF VANES, PROJECTING INTO ELECTRON BEAM, TAPERED TO REDUCE BEAM INTERCEPTION Filed. Feb. 25, 1963 FIG.2

INVENTORS ROBERT G.ROCKWELL ADOLPH J. FIEDOR BY FIG.5 V

ATTORNEY United States Patent M 3,243,641 ELECTRON TUBE APPARATUS HAVING GRID CONSISTING OF VANES, PROJECTING INTO ELECTRON BEAM, TAPERED T0 REDUQE BEAM INTERCEPTION Adolph J. Fiedor, Palo Alto, and Robert G. Rockwell, Menlo Park, Calif., assignors to Varian Associates, Palo Alto, Calif., a corporation of California Filed Feb. 25, 1963, Ser. No. 260,817 14 Claims. (Cl. 315-557) The present invention relates in general to high frequency tube apparatuses and more particularly to improved electron permeable metallic grid structures for electrically coupling to electron beams. Such improved grid structures provide increased transparency and coupling efiiciency and are especially useful, for example, as resonator grids in klystron beam tubes to increase tube gain, efficiency and power output.

Heretofore klystron beam tubes of low to moderate RF. power output, i.e., up to in the order of 100 watts continuous R.F. output at gc. have employed gridded electron permeable cavity resonators. The cavity resonators have been provided with axially aligned electron permeable gridded wall portions through which the beam is directed for interaction with the electric fields of the cavity resonators.

A typical prior art grid structure included a plurality of J-shaped radially directed metallic vanes of a refractory metal as of tungsten carried at their base or short leg portion from a good thermally conductive metallic circular channel forming a support ring. The vanes at X-band frequencies were relatively thin as of 0.001 thickness with a height, taken in the direction of beam travel, of approximately 0.020". In an improved grid structure, described and claimed in a copending application U.S. Serial No. 48,889 filed August 11, 1960 of Adolph J. Fiedor et al., now issued as US. Patent 3,104,341 and assigned to a common assignee, the vanes were raised above the support ring by a substantial amount as of three quarters of their height to minimize stray capacity between mutually opposed grid vane support rings. This stray ring capacity lowers the coupling efficiency of the cavity resonator by providing substantial stray capacity external of the beam thereby lowering the R,,,/ Q ratio, where R is the shunt resist ance of the cavity and Q is the Q of the cavity.

In the present invention the long leg portion of the grid vanes are tapered in height such as to reduce their height taken in a radial direction toward the center of the beam. Tapering the vane height reduces beam interception by giving the grid structure increased transparency to non-axially aligned beam particle trajectories. In addition the short leg portion of the L-shaped vanes is tapered in height to reduce stray capacity between mutually opposed grid vane structures thereby increasing coupling efficiency by increasing the R /Q ratio of gridded cavity resonators.

The principal object of the present invention is to provide an improved high frequency electron discharge device having increased gain, efficiency and power output.

One feature of the present invention is the provision of an electron permeable metallic grid structure having a plurality of vanes directed inwardly of an electron beam path wherein the vanes are tapered with decreasing height taken in a direction toward the center of the beam path to reduce beam interception.

Another feature of the present invention is the provision of a metallic electron permeable grid structure including a plurality of vanes with body portions inwardly directed of a beam path and carried in a raised position from and above a support ring via support leg portions 3,243,641 Patented Mar. 29, 1966 wherein the support leg portions are tapered in height with decreasing height taken in a direction away from the body portion of the vanes to reduce stray capacity between opposed grids.

Another feature of the present invention is the provision of a gridded cavity resonator including a pair of spaced apart electron permeable grid structures as called for in the preceding features wherein the body portions of the vanes are registered taken in the direction of the beam path, to reduce beam interception and the support leg portions are positioned out of registry to reduce stray capacity and to increase the R /Q of the cavity.

Another feature of the present invention is the provision of a gridded cavity resonator including a pair of spaced apart electron permeable grid structures each grid structure being defined by a plurality of inwardly directed sheet-like vanes each vane having an elongated central body portion inwardly directed of the beam path, and the grid structures being formed such that the axial spacing between the central portions of the grid structures is less than the spacing between the outer portions of the central body portions of the grid structures whereby stray capacity of the grids is reduced.

These and other features and advantages of the present invention will be more apparent after a perusal of the following specification taken in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of an electrostatically focused four-cavity klystron amplifier embodying features of the present invention,

FIG. 2 is an enlarged partial longitudinal cross-sectional view of the structure shown in FIG. 1 taken along line 22 in the direction of the arrows,

FIG. 3 is a cross-sectional view of a portion of the structure shown in FIG. 2 taken along line 33 in the direction of the arrows and showing the novel grid structure of the present invention,

FIG. 4 is an enlarged fragmentary perspective view of a portion of the structure of FIG. 3 delineated by line 4-4,

FIG. 5 is an enlarged fragmentary side view of the opposed cavity resonator grid structure of FIG. 2 taken along line 5-5 in the direction of the arrows of FIG. 3, and

FIG. 6 is an enlarged fragmentary perspective view of a grid vane structure of the present invention alternative to that structure shown in FIG. 4.

Referring now to FIGS. 1 and 2 there is shown a multicavity klystron amplifier tube 1 utilizing features of the present invention. More particularly, the tube 1 includes a central metallic block body portion 2 as of aggregate iron and copper material having a centrally disposed axially directed bore 3 therethrough.

A conventional electron gun assembly 4 is affixed as by brazing to one end of said central body portion 2 in axial alignment with said bore 3 for forming and projecting a pencil-like beam of electrons over an elongated beam path 5 axially of said bore 3. A conventional beam collector structure 6 is affixed as by brazing to the central body at the end thereof remote from the gun 4 for collecting the beam of electrons.

A plurality of re-entrant cavity resonators 7 are disposed along the beam path 5 intermediate the electron gun 4 and the collector 6 for electromagnetic interaction with the beam of electrons passable therethrough. An input terminal is provided by input waveguide 8 for applying signals, to be amplified, to the beam via the intermediary of the upstream cavity resonator 7 coupled to the waveguide 8 via a suitable coupling iris 9.

An output terminal, for extraction of amplified microwave signals from the beam, is provided by output waveguide 11 coupled to the down stream resonator 7 via an output coupling iris, not shown. The central body 2, electron gun 4, collector 6, cavities 7, and waveguides 8 and 11 are all evacuated. The waveguides 8 and 11 are provided with vacuum tight R.F. windows 12 as of alumina ceramic sealed across the guides 8 and 11 for holding the vacuum while permitting passage of microwave energy therethrough.

The cavity resonators 7 are defined by the region of space bounded by axially spaced apart transverse metallic end walls 13 and the side walls of the axial bore 3 intermediate the spaced transverse walls 13. The end walls 13 are provided with a plurality of centrally disposed axially aligned bores 14 defining a plurality of RF. field free drift tubes 15 through which the beam passes between resonators 7.

The ends of the drift tubes 15 project into the cavity resonators 7 in re-entrant fashion and are capped at their ends by electron permeable metallic grid structures 16 for increasing the electric coupling to the electrons of the beam.

The grid structures 16 are best seen by reference to FIGS. 3-5 and comprise a plurality of generally L-shaped metallic vanes 17 as of tungsten. The vanes 17 are made of relatively thin gauge sheet stock as of 0.001" thick with a height, h, taken in the direction of beam travel, many times their thickness as of twenty times their thickness.

The L-shapecl vanes are formed with a relatively long body portion 18 having a length, l, as of sixty times their thickness and a shorter base leg portion 19 of a length as of twenty times their thickness. The base leg 19 is turned and extends away from the body portion 18 approximately at right angles to the plane of the body portion 18 of the vane 17. The vanes are carried from a metallic support ring 21 as of aggregate tungsten and copper by being brazed thereto along abutting edges of the base leg portion 19.

The grid vane 17 is preferably mounted from the support ring 21 in a raised manner, i.e., with a substantial portion of the grid height, as of at least 10% of h, rising above the support ring 21. This raised grid structure 16 minimizes stray capacity between support rings 21 when two such grid structures 16 are positioned in axially spaced registry as when mounted over the ends of mutually opposing re-entrant portions of cavity resonator drift tube segments 15. Typical spacing between mutually opposed long body portions 18 is one radian of transit angle. In a typical X-band tube this gap spacing is 0.018".

The grid vane 17 is, of course, mounted with the plane of the main body 18 parallel to the beam axis, and thus the electron trajectories, to minimize beam interception. The vane bodies 18 project radially inwardly toward the beam axis from the surrounding support ring 21.

In a preferred embodiment of the present invention the vane height at the innermost end or tip of the vane is less than the vane height, h, at the base end of the main body 18 of the vane 17 to further reduce beam interception. The reduced vane height provides higher grid transparency to electrons having trajectories out of alignment with the beam axis 5. A typical reduced vane height at the innermost end is one fifth the full vane height.

The reduced vane height is conveniently provided by tapering the vane height at 22 from the reduced height at the vane tip to the full vane height at a point midway of the length of the main body 18 of the vane 17 to permit increased thermal conduction and mechanical strength of the vane taken in the direction toward the support ring 21. The tapered portion 22 of the main vane body 18 is preferably provided on the bottom edge of the vane 17 or on the edge remote from axially spaced mutually opposed grid structure 16 to prevent reduction of capacity between axially spaced apart mutually opposed top edges of the main body portion 18 of the vanes 17. It is desired to maximize the mutual capacity between mutually 4 opposed grid structural portions 18 which are immersed in the beam path to obtain optimum electrical coupling to the beam with minimum beam interception.

The base leg 19 of the vane 17 is likewise tapered in height at 23 from a full height, at the junction of the base leg portion 19 with the main body portion 18, to zero height relative to the support ring 21 at the outer end of the base leg 19. This reduction in height at the top edge of the base leg portion 19 of the vane 17 reduces the undesired stray capacity between mutually opposed axially spaced base leg portions 19 of similar grid structures 16.

In a preferred embodiment of the present invention the axially spaced apart similar grid structures 16 are arranged and aligned, as best seen in FIG. 5, such that the main body portions 18 of the spaced apart opposed vanes 17 are in registry, taken in a direction along the beam axis 5. This registry serves to maximize mutual capacity between the main body portions 18, which body portions are immersed in the beam to yield optimum beam couling.

p However, the tapered base leg portions 19 are arranged in axially interdigitated alignment or in other words, out of registry to minimize unwanted mutual stray capacity between axially spaced apart opposed grid structures 16. This latter effect is obtained by having the base legs 19 of one grid structure directed around the support ring in a clockwise direction while the opposed grid structure has the base legs directed around its support ring in a counter clockwise direction when viewed down the axis of the beam 5 through a pair of opposed grid structures 16. However, the alignment can he obtained by one grid geometry because identical grid structures 16, when faced in opposite directions in mutually opposed relation, as found in the re-entrant gap of a cavity, provide this preferred out of registry alignment of the "base legs.

Improved results are obtained by use of grids made in accordance with provisions of the present invention. For example, an X- band klystron amplifier using grids having tapered main bodies '18 and tapered base leg 19 performed at 18% etficiency with 100 watts maximum continuous output RF. power whereas an identical tube, except that it employed untapered grids, performed at 12% efiiciency and with a maximum power output of 75 watts. Thus, the tapered grids of the present invention increased the R.-F. efliciency by 50% and the power output by 33%%. The improvement in gain was from 32 to 37 db in this example.

Referring now to FIG. 6 there is shown an alternative grid vane stnucture of the present invention. In this embodiment the central beam immersed portion of the grid vane is raised with respect to the outer main body portion of the vane body, base leg and support ring in order to further reduce stray capacity of the vanes and support ring.

More specifically, the sheet-like vanes 25 include an elongated central body portion 26 and a shorter base leg portion 27 turned approximately 90 degrees to the plane of the central body portion 26. A support ring 28 surrounds the inwardly directed central body portions 26 and supports the vanes 25 from the base leg portions 27 as by being brazed thereto. The central body portions 26 of the vane are shaped and arranged with respect to the support ring such that the central body portions 26 of the vanes have a height above the support ring 28 at their innermost region 29 greater than the height above the support ring for their outermost region 31 whereby stray capacity of the grid vanes 25 and support rings 28 is reduced.

For a pair of mutually opposed grid structures 16 utilizing the vane geometry of FIG. 6, the spacing between the central portions of the grid vane central body 29 is less than the outer portions of the grid vanes 31 thereby reducing the stray capacity of a cavity resonator using such electron permeable grid structures.

In a preferred embodiment of the structure of FIG. 6 the height of the vanes 26 increases outwardly of the beam to decrease beam interception and to increase thermal conduction and strength.

Although the novel grid structure of the present inven tion has been described as it relates to a multicavity klystron amplifier it is also applicable to other types of high frequency beam tubes such as reflex tubes, traveling wave tubes, etc.

Since many changes can be made in the above construction and many apparently widely diiferent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. -A high frequency electron tube apparatus including, means for forming and projecting a beam of electrons over an elongated beam path, means arranged along the beam path in energy exchanging relationship therewith, said energy exchanging means including an electron permealble metallic grid structure, said grid structure including a plurality of metallic vanes projecting into said beam path, said vanes being of sheet-like geometry with a maximum height taken in the direction of the beam path of at least five times the sheet thickness and disposed with the plane of the sheet shaped vanes being substantially parallel to the direction of the beam path, and said vanes having a height internally of the beam path substantially less than the maximum height of said vanes externally of the beam path wlhereby beam interception by said vanes is reduced over vanes of uniform height.

t2. The apparatus according to claim 1 wherein said vanes are tapered in height to a reduced height internally of the beam.

'3. The apparatus according to claim 1 wherein a plurality of said vanes have an elongated main body portion projecting into the beam and a shorter base support portion turned at a substantial angle to the main body portion for supporting said vane in position, and the height of said base portion decreasing in a direction taken away from the main body portion of said vanes for decreasing the stray capacity of said vanes.

4. The apparatus according to claim 2 wherein said vanes are supported externally of the beam by a support ring surrounding the beam path with said vanes projecting into the beam from said support ring, and said vanes having a height where affixed to said support ring substantially rising above said support ring to decrease the stray capacity of said support ring.

5. The apparatus according to claim 3 including a sup port ring surrounding said beam path and carrying said vanes from said base portion with said main body portion of said vanes projecting radially inwardly of said beam path, said vanes terminating internally of the beam path, and said base portions of said vanes having a preponderance of their maximum height rising above said support ring to reduce the stray capacity of said support ring.

6. High frequency electron tube apparatus including, means for forming and projecting a beam of electrons over an elongated beam path, a cavity resonator arranged along the beam path in energy exchanging relationship with the beam, said cavity resonator having a pair of mutually opposed electron permeable wall portions for passage of the electron beam through said cavity resonator, said electron permeable wall portions of said cavity resonator including a pair of mutually opposed grid structures, said grid structures including a plurality of metallic vanes projecting into said beam path, said vanes being of sheet-like geometry with a maximum height taken in the directon of the beam path of at least five times their thickness and disposed with the plane of said sheet vanes being substantially parallel to the direction of the beam path, and said vanes having a height internally of the beam path substantially less than the maximum height of said 'vanes externally of the beam path whereby beam interception by said vanes is reduced over vanes of uniform height.

7. The apparatus according to claim 6 wherein each of said grid structures includes a support ring surrounding said beam path and carrying said vanes such as to project radially inwardly of said beam path, said vanes terminat ing internally of the beam path and said vanes having a preponderance of their maximum height rising above said support ring taken in a direction toward the opposing grid structure to reduce the stray capacity of said support ring.

8. The apparatus according to claim 7 wherein said vanes have a height which is tapered and increases taken in a direction from the terminating internal ends thereof toward said support ring to increase the thermal conductivity of said vanes, and to increase the mechanical strength of said vanes.

9. The apparatus according to claim 8 wherein said vanes include an elongated main body portion projecting into the beam and a shorter base support portion turned at a substantial angle to the main body portion of the vane for supporting said vanes from said support ring, and wherein the height of said base support portion is reduced taken in a direction along the base support portion away from the main body portion of said vane to reduce the stray capacity of said vanes.

10. The apparatus according to claim 9 wherein said main body portions of said mutually opposed radially di rected vanes are axially aligned in registry to reduce beam interception.

11. The apparatus according to claim 10 wherein said registered vanes include base support portions disposed out of registry to further reduce stray capacity of said vane structures.

12. The apparatus according to claim 10 wherein said tapered portions of said mutually opposed grid structures are formed by removing material substantially only from the remote edges of the mutually opposed vanes.

13. A high frequency tube apparatus including, means for forming and projecting a beam of electrons over an elongated beam path, a cavity resonator positioned along the beam path for interaction with the beam passable therethrough, said cavity resonator having a pair of electron permeable wall portions axially spaced apart in the direction of the beam path for passage of the beam through said resonator, said pair of electron permeable wall portions being defined by a pair of metallic grid structures, each of said grid structures including a plurality of sheet-like vanes having central body portions projecting inwardly of the beam path from a surrounding support structure, and said inwardly projecting central body portions of said vanes being mounted from said surrounding support structure such that the innermost portions of said inwardly directed central body portion of said grid vanes have a height above the surrounding support structure greater than the height of an outer portion of said inwardly directed central body portions of said vanes above said support structure such that the axial spacing between the central portions of said mutually opposed grid structures is less than the axial spacing between outer portions of said grid structures in order to reduce stray capacity of said grid structures.

14. The apparatus according to claim 13 wherein the height of said inwardly directed central body portions of said grid vanes increases in a direction taken outwardly of said beam path whereby beam interception by said vanes is reduced.

No references cited.

HERMAN KARL SAALBACH, Primary Examiner. R. D. COHN, Assistant Examiner. 

1. A HIGH FREQUENCY ELECTRON TUBE APPARATUS INCLUDING, MEANS FOR FORMING AND PROJECTING A BEAM OF ELECTRONS OVER AN ELONGATED BEAM PATH, MEANS ARRANGED ALONG THE BEAM PATH IN ENERGY EXCHANGING RELATIONSHIP THEREWITH, SAID ENERGY EXCHANGING MEANS INCLUDING AN ELECTRON PERMEABLE METALLIC GRID STRUCTURE, SAID GRID STRUCTURE INCLUDING A PLURALITY OF METALLIC VANES PROJECTING INTO SAID BEAM PATH, SAID VANES BEING OF SHEET-LIKE GEOMETRY WITH A MAXIMUM HEIGHT TAKEN IN THE DIRECTION OF THE BEAM PATH OF AT LEAST FIVE TIMES THE SHEET THICKNESS AND DISPOSED WITH THE PLANE OF THE SHEET SHAPED VANES BEING SUBSTANTIALLY PARALLEL TO THE DIRECTION OF THE BEAM PATH, AND SAID VANES HAVING A HEIGHT INTERNALLY OF THE BEAM PATH SUBSTANTIALLY LESS THAN THE MAXIMUM HEIGHT OF SAID VANES EXTERNALLY OF THE BEAM PATH WHEREBY BEAM INTERCEPTION BY SAID VANES IS REDUCED OVER VANES OF UNIFORM HEIGHT. 